Therapeutic proteins may at times during the course of manufacturing, handling, storage, and administration be exposed to visible light and ultraviolet radiation. Protecting proteins from light exposure has typically involved physically covering the sample with foil, or a box or other container, or by storage in a closed refrigerator. There may be times, however, when exposure of the protein to light may be unavoidable and as a result of this exposure, the protein may become degraded. Light induced degradation of proteins can involve the oxidation of several amino acids including tryptophan, tyrosine, methionine, histidine, and cysteine. If the oxidation alters the protein's structural properties, it may lose biological activity. The oxidation of certain amino acid residues may also lead to yellowing of the protein solution. Moreover, the oxidized protein may aggregate through disruption of native disulfide bonds or through the formation of dityrosine linkages. The loss of biological activity, change in color and/or clarity of the protein solution, and formation of aggregates are commercially undesirable effects. In extreme cases the oxidation or aggregation could cause an immunogenic response in patents with possibly severe side effects.
In addition to free radicals generated by light exposure, proteins may be formulated with excipients containing small amounts of impurities which, although harmless themselves, could generate free radicals that hasten degradation and/or oxidation of proteins. Protein formulations in pre-filled syringes and other drug delivery devices may contain extractables or metal ions which could catalyze free radical generation and protein oxidation. Approved excipients for use in protein formulation may be limited in their ability to prevent these types of oxidation.
Various types of molecules such as sugars, surfactant, amino acids and fatty acids have been used in efforts to stabilize protein and peptide products against degradation. See Wang and Hanson, J. Parenteral Science and Technology Supplement, 1988, Technical Report No. 10 (describing parenteral formulations of proteins and peptides); Manning et al., 6 Pharmaceutical Research, 1989. Examples of excipients such as buffers, preservatives, isotonic agents, and surfactants are also known in the art. See 21 C.F.R.sctn.180.22 et seq. (defining recognized food additives); Wang and Kowal, 34 J. Parenteral Drug Association 452, 1980 (describing various excipients); A. R. Gennaro et al., 17th Remington's “Pharmaceutical Sciences.” 1985; Avis et al., Pharmaceutical Dosage Forms: Parenteral Medications, Vol. 1, 1992, all of which, including the definitions of various useful excipients, are hereby incorporated by reference herein.
It is understood that the development of a suitable aqueous formulation for administration to a subject is complex. A need exists in the art for aqueous formulations of therapeutic proteins having minimal physical and chemical degradation when exposed to varying levels of UV radiation or other light, or when exposed to other sources that generate free radicals.